This application claims the benefit of Japanese Patent Application P 2002-75, 818 filed on Mar. 19, 2002, the entirety of which is incorporated by reference.
1. Field of the Invention
The present invention relates to a semiconductor mounting system.
2. Related Art Statement
In a semiconductor processing such as CVD, sputtering and etching, a semiconductor wafer is mounted on a so-called susceptor, which is then heated to carry out the heat treatment of the wafer. It has been known that an electrostatic chuck made of a ceramic material is used as a susceptor for adsorbing a semiconductor wafer and heated for subjecting the wafer to a heat treatment. It is, however, necessary to reduce the temperature change during the adsorption-desorption cycles of semiconductor wafers on a susceptor, for further improving the production of the semiconductor wafers. It is therefore needed to control and switch the heating and cooling of the wafer with a reduced time delay. The necessity of controlling the heating-cooling cycle demands a cooling system connected with the susceptor.
In Japanese Patent Publication 287, 344A/1992), paste of an adhesive composition made of silicone resin is used to join a susceptor and a metal cooling flange. Further in Japanese patent publication 45, 757A/1997, a susceptor and a metal cooling board is joined with indium metal.
When indium or adhesive resin composition is used for joining a ceramic electrostatic chuck and a water cooling flange of a metal, however, an insufficient pressure during the joining process may reduce the flatness of the adsorption face of the chuck for a semiconductor wafer. When a semiconductor wafer is processed, the wafer is adsorbed onto the adsorption face of the electrostatic chuck. The chuck having an adsorption face with a deteriorated flatness may thus not be used and the production yield may be reduced. Further, back side gas is supplied over the surface of an electrostatic chuck in many cases, it is difficult to maintain the air-tightness of the joining portion between the chuck and metal member. Thermal cycles are applied on a semiconductor production system. It is particularly needed to maintain the air-tightness of the joining portion at excellent reliability after the thermal cycles. On the contrary, if the pressure during the joining process is too high, the adhesive composition may be out of the joining portion flown along the interface between the chuck and cooling flange. Further, the thickness of the adhesive layer may not be uniform or changed in different articles. In this case, the thermal conductivity between the semiconductor mounting and metal members may be changed to reduce the production yield.
Further, an adhesive of silicone resin composition does not have an elongation sufficient for relaxing the thermal stress to induce warping or peeling of the joining face after the joining process.
An object of the present invention is to provide a novel semiconductor mounting system having a semiconductor mounting member, a metal member and a joining layer joining the mounting and metal members, to improve the flatness of a semiconductor mounting surface and to enable the temperature control of a semiconductor surface.
The present invention provides a semiconductor mounting system having a semiconductor mounting member with a surface for mounting a semiconductor, a metal member and a joining layer joining the mounting and metal members. The joining layer is composed of an adhesive sheet having a resin matrix and a filler dispersed in the matrix.
The inventor has tried to use an adhesive composition for the adhesive layer. In this case, however, the adhesive composition has fluidity and may be flown out of the joining portion when a pressure is applied. It is thus difficult to improve the flatness of the joining adhesive layer by applying a sufficient pressure. An adhesive sheet made of resin matrix is already hardened before interposed between the mounting and metal members. Such resin matrix does not pressed out from the joining layer when a pressure is applied during a heat treatment. It is thus possible to apply a sufficient pressure during the joining process and to improve the flatness of the mounting surface of the mounting member.
The adhesive sheet is made of a resin matrix, however, and has a low thermal conductivity. The adhesive sheet further has a some degree of thickness. The thermal conductivity in the joining layer may not be made sufficiently high to escape heat generated in the wafer surface through the joining layer. The temperature on the semiconductor surface may be too increased.
The inventor has reached the idea of adding a filler in the adhesive sheet. It is possible to improve the thermal conductivity of the joining layer by adding a filler in the adhesive sheet. It is thus possible to improve the flatness of the surface of the semiconductor mounting member and to control the temperature on the semiconductor surface at the same time.
Preferably, the filler is made of a material having a thermal conductivity higher than that of the resin matrix. The thermal conductivity of the adhesive sheet may be improved by adding a filler, to the matrix, made of a material having a thermal conductivity higher than that of the matrix.
Further, the Young""s modulus of the adhesive sheet may preferably be not higher than 100 MPa and the elongation of the sheet may preferably be not lower than 100 percent and more preferably be not lower than 150 percent. The adhesive sheet having such improved flexibility may be effective for maintaining the air-tightness between the semiconductor mounting and metal members. The elongation or deformation of the adhesive sheet may be also effective for reducing the thermal stress. It is thus possible to prevent the warping of the joined body or peeling of the joining layer due to thermal stress after the joining process.
The elongation of the adhesive sheet is measured as follows.
An adhesive sheet having a width of 25 mm is clamped with a jig at its upper and lower ends. The distance between the clamped points at the upper and lower ends (clamp distance) is adjusted to 100 mm. The upper and lower ends are pulled at a speed of 300 mm/minute till the adhesive sheet is cut. The elongation is defined as follows.
xe2x80x9cElongationxe2x80x9d=(xe2x80x9cdistance between the upper and lower ends at the moment the sheets is cutxe2x80x9d minus 100 mm)/100 mmxc3x97100 percent.
These and other objects, features and advantages of the invention will be appreciated upon reading the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes of the same could be made by the skilled person in the art.